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BB1702 Biochemistry: Structure and Function > Enzymes-1 > Flashcards

Flashcards in Enzymes-1 Deck (27)
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1

Where on an enzyme does catalysis occur?

The active site

2

What do proteolytic enzymes catalyse?

Proteolysis (hydrolysis of a peptide bond)

3

What small molecules are sometimes present in enzymes and essential for some enzymes to work?

Cofactors

4

What is an enzyme without its cofactor called?

An apoenzyme

5

What is an enzyme with its cofactor called?

holoenzyme

6

Apoenzyme + cofactor =

Holoenzyme

7

What are the two subdivisions of cofactors?

  1. Metals
  2. Coenzymes

8

What are tightly bound coenzymes called?

Prosthetic groups

9

Define free energy (G)

A thermodynamic property that is a measure of useful energy , or the energy that is capable of doing work

10

What happens in a reaction that has -ΔG?

It is spontaneous

11

What happens in a reaction that has +ΔG?

It is not spontaneous

12

What is the difference in energy between the substrate and the transition state?

The activation energy

13

The active site of an enzyme is the region that binds the ________ (and the _______, if any). It also contains the residues that directly participate in the ________ and _________ of bonds. These residues are called the _________ _______.

The active site of an enzyme is the region that binds the substrates (and the cofactor, if any). It also contains the residues that directly participate in the making and breaking of bonds. These residues are called the catalytic groups.

14

What are some of the generalisations that can be made about the active sites of enzymes?

  • the active site has a three-dimensional cleft
  • the active site takes up a small portion of the total volume of the enzyme
  • active sites are unique microenvironments
  • substrates are bound to enzymes by multiple weak attractions
  • the specificity of binding depends on the precisely defined arrangement of atoms in an active site

15

What is the velocity of an enzyme catalysed reaction?

The amount of product formed in a given amount of time, or the amount of substrate that disappears in a unit of time

16

What is the Michaelis-Menten equation?

17

What is the Michaelis constant, KM?

18

How can Kbe worked out from a V0/[S] graph? 

19

Define Vmax

The point at which there is a maximal turnover of product from an enzyme, i.e. the enzyme is fully saturated with substrate

20

Define KM

A constant that describes the amount of substrate needed to half saturate an enzyme. A high Kmeans a lot of substrate is needed to saturate an enzyme.

21

What Kcat?

A constant that describes the turnover number of an enzyme

22

What is a Lineweaver-Burk plot?

A plot of 1/V0 versus 1/[S].

Can be used to determine Vmax as the y intercept is 1/Vmax

23

What are the two main types of inhibition of an enzyme?

  1. Reversible
  2. Irreversible

24

What are the three types of reversible enzyme inhibition?

  1. Competitive
  2. Noncompetitive
  3. Uncompetitive

25

How does competitive inhibition affect Vmax and KM?

Vmax is unchanged

KM is decreased

26

How does uncompetitive inhibition affect Vmax and KM​?

Vmax is decreased

KM is decreased

27

How does noncompetitive inhibition affect Vmax and KM​?

Vmax is decreased

KM is unchanged